This invention generally relates to apparatus for determining the direction of a remotely located signal source and, more particularly, to apparatus including underwater sensors for determining the bearing of a remotely located source of acoustic signals.
The tracking of submarines and the like as by sensing acoustic signals of characteristic frequencies emanating from the submarine and determining bearing of the submarine with sonobuoys involves positioning of a hydrophone array at some depth beneath the ocean surface. In direction determining apparatus of the type including an omnidirectional hydrophone and a pair of orthogonally mounted directional hydrophones whose output signals are processed as by comparing the phase of a combination of the directional signals with the phase of the omnidirectional signal, it is critical that the channels carrying the omnidirectional and directional signals to a surface located transmitter be exactly matched in phase shift characteristics. At depths of several tens of feet, the problems in maintaining precise phase shift characteristics are considerable.